The present invention relates to novel electrostatic charge transfer media and a method for preparing said media. Plasma treatment (generated by radio frequency R.F., alternating current A.C., microwave, or direct current D.C.) of suitable polymers produces a modified polymer surface that provides improved transfer of electrostatic charge from a donor surface to a receptor surface.
Over the past several decades, organic polymers have been extensively utilized to produce articles such as films, sheets, coatings, tapes, or cloths, and are particularly desirable because of their superior physical and chemical properties in such areas as electrical characteristics, thermal characteristics, chemical resistance, shatter resistance andd flexiblity. However, because their surface is inert and insulative, electrostatic charge transfer to such a surface is inefficient.
The transfer of electrostatic images from one surface to another, for example, from an electrophotographic plate to a dielectric surface, provides a method of electrostatic printing or copying wherein the latent electrostatic charge pattern is not directly developed to visible form on the electrophotographic plate or drum. This eliminates the need for cleaning the electrophotographic plate or drum, thereby eliminating the need for cleaning devices, and consequently improving the life of plates and drums and reducing the maintenance requirements. An added advantage of the charge transfer process is that the transferred electrostatic charge image is stable (no dark decay as seen on electrophotographic substrates) and may be developed off-line up to 4 days after transfer. Processes known in the prior art for the transfer of electrostatic images (an art at times referred to by the acronym, TESI) have found practical applications in commercial electrophotographic or electrostatic printing only for low resolution images.
In electrophotography or electrostatic printing, the prior art techniques for accomplishing charge transfer from one surface to another involves either: (1) conduction of electric charges across an air gap, or (2) direct charge transfer if the air gap is eliminated. While the air breakdown charge transfer technique is simple, it does not provide high resolution (less than 80 line pairs per millimeter (lp/mm) can be achieved) or continuous tone gray scale reproduction. Finally, this technique also requires the donor surface to sustain high surface potentials to insure air breakdown. The presently known techniques for direct charge transfer require a very smooth surface, a transfer liquid interfacing the donor and receptor films, very high pressures to eliminate the air gap, or a surface provided with a multitude of conductivity sites, as described in U.S. Pat. No. 4,454,186. Even though high resolution exceeding 200 lp/mm charge transfer has been claimed, the transfer speed is too low, and the charge transfer efficiency is too low for certain types of imaging procedures, particularly when the transfer of charge is required in a short time interval, e.g., less than 0.1 sec. In many commercial applications, for example, duplication of customers' checks by banks, transfer of charge must be accomplished within an extremely short time interval. Accordingly, there remains a need for a simple means of making high resolution charge transfer images with gray scale fidelity, high transfer speed, and high transfer efficiency.